The invention relates to an improved three dimensional blade for axial steam turbine particularly to the aerodynamic improvement of moving blades pertaining to entry stages of axial steam turbine.
A conventional blade known as cylindrical blade, is cylindrical in shape and made of a constant cross-section throughout the blade height.
The invention primarily relates to moving blade of axial steam turbines, but the principle and design procedure are applicable for also to fixed blades, known as guide or stationary blades. The term xe2x80x98turbine bladexe2x80x99 is used in the description to denote aerofoil blades. The efficiency of turbine is of paramount importance for cheaper power generation. The blades are supposed to be most crucial apart from stationary flow path components for efficiency of the turbine.
The conventional blades is of constant cross section and cylindrical in shape over the blade height. The U.S. Pat. No. 5,779,443 which was granted in 1998 is one such belonging to prior art in this area. At any cross section the shape of the profile remains same.
There are disadvantages associated with steam turbine runner blades in high and intermediate pressure cylinders are of low height and low aspect, and many a time employ cylindrical blades and in such a blade row the losses due to secondary flow are significant. The secondary flow is opposed to main flow in direction and caused due to turning of boundary layer along the hub and casing.
Therefore, the main object of the present invention is to propose an improved blade to reduce the losses by leaning and twisting the blade profiles so as to have aft-loaded blade instead of centrally loaded one at sections near root and tip. According to the present invention there is provided an improved three dimensional blade for axial steam turbine comprising a leading edge for inlet flow and a trailing edge for an angle, a pressure face, suction face and a chord which is the line connecting the leading and trailing edge and the betabi, the stagger angle formed at the intersection of said chord and U-axis wherein the blade is made of varying cross-sections of profiles hub to tip and leaned such that the centre of gravity of mid sections are shifted opposite to the direction of blade rotation and the blade sections from hub to tip are twisted in a gradual manner.